This is a proposal for a preliminary histological and electrophysiological study of the visual system of triploid frogs (i.e., frogs whose cell nuclei each have three sets of chromosomes instead of two). The unusual properties of triploids make them ideal for investigations into the factors which determine the extent of branches of nerve cell dendrites and axon terminals; this branching in turn determines the possible input and output connections of the nerve cell. The research proposed here is designed to answer two questions, and to begin answering a third: (1) How do cell size and cell number in triploid neural tissue, specifically retina and tectum, compare to the values found in similar diploid tissue? (2) What effect does triploidy have on the length and diameter of dendrites and axons, and on the structural characteristics of dendritic branches and axon terminal arborizations? (3) What effect does triploidy have on the receptive field characteristics of retinal ganglion cells? Triploid frogs are produced by a standard method involving heat- shocking eggs after fertilization. Cell size and number will be measured directly by serial sectioning and light microscope examination. Golgi staining will be used to measure dendritic branching. The extent of axon terminal arborization will be determined by an electrophysiological method previously developed by the principal investigator. Finally, receptive field mapping will be accomplished by single unit recording from ganglion cells, presentation of computer- generated visual stimuli, and computer-generated visual stimuli, and computer analysis of the resulting spike responses. For each procedure, results from triploids will be compared with those from diploids at a similar stage of development. This research will provide the basis for an extensive study of visual system development and physiology in triploid animals.